Semi-conductor rectifier assemblies



Nov. 15, 1960 P. M. TIPPLE 2,950,539

SEMI-CONDUCTOR RECTIFIER ASSEMBLIES Filed June 4, 1959 7 7 fl i I 2INVENTOE fimm z w 8Y5 Z V?" TTORNEYS SEMI-CONDUCTOR RECTIFIER ASSEMBLIESPeter Moi-land Tipple, Ruisiip, England, assignor to Enghsh ElectricValve Company Limited, London, England, a British company Filed June 4,1959, Ser. No. 818,187 Claims priority, application Great Britain July2, 1958 2 Claims. (Cl. 317234) This invention relates to semi-conductorrectifier assemblies and more specifically to semi-conductor rectifierassemblies of the kind in which the rectifier propera germanium or asilicon rectifieris housed within an hermetically sealed, gas filledenvelope.

According to this invention a semi-conductor rectifier assemblycomprises a rectifier proper mounted in an hermetically sealed envelopewhich also houses a body of solidified desiccant material.

A preferred desiccant material is aluminum sodium silicate which hasbeen subject to molecular sieving and solidified. Such a body iscomparatively free from liability to the formation of desiccant dust.

Preferably the body is a pre-cast ring or cylinder or solidifieddesiccant material. Where, as is commonly the case in practice, thehermetically sealed envelope comprises metal parts which are brazed orotherwise fixed to one another (to complete the envelope) by a heatingprocess involving the application of high temperature, the desiccantring or cylinder is preferably positioned between the rectifier properand the areas at which said parts are so fixed to one another so as toprovide a measure of shielding of the said rectifier proper from vapourswhich may be produced by the high temperature heating process.

The invention is illustrated in the accompanying drawings which show,partly in section, two embodiments thereof. Like references indicatelike parts in both figures.

Referring to Figure 1, the assembly therein shown comprises a rectifierjunction I mounted in the usual way on the customary heavy copper heatsink base 2 between the upper face of said base and the usual top piece3. The latter is of rectangular section being narrower in the directionat right angles to the plane of the paper than it is in the direction ofsaid plane. An hermetically sealed envelope is completed by means ofmetal members 4, 5, 6 and 7 and a glass ring 8. The approximatelycylindrical member 4 is welded to the top piece 3 near the bottom edgethereof; the approximately annular member 7 is welded to the undersideof a top flange on the member 2; the parts and 6 are fused each at oneend into opposite ends of the glass ring 8; and the remaining ends ofthe parts 4 and 5 and the remaining ends of the parts 6 and 7 are brazedtogether as shown in a final brazing operation to complete the enevlope.An exhaust tube 9 enables the device to be pumped out and filled with asuitable dry gas.

In accordance with this invention a ring of solid desiccant material,pre-cast to a desired shape, such as that shown, and made, for example,of molecular sieved aluminium sodium silicate pre-cast into the solidbody, is provided at it). After pumping out and filling with gas, thetube is, of course, pinched off in the usual way.

The desiccant ring serves the important purpose of maintaining theinterior of the envelope in a dry state during the life of the device.Careful research has shown that the maintenance of a high degree ofdryness is very important to good performance, probably more importantthan the choice of the gas used. Known gas filled rectifier assemblieshave fallen far short of the desired maintenance of a high degree ofdryness principally because it is in practice almost impossible to avoidthe release, during the life of the device, of small quantities of watervapour occluded by metal surfaces inside the envelope. Accordingly, eventhough great care is taken in manufacture of a known device to ensurethat the gas filling is dry when it is put into the envelope, it all toooften happens that when the device has been in use some time the gasfilling is no longer of the required dryness. The ring 10 of solidifieddesiccant provided in accordance with this invention acts as a getterfor water Vapour that may be released during the life of the device. Thefact that the ring is of solidified desiccant material eliminates orreduces to negligible proportions the risk of powdered desiccant comingnear or in contact with the rectifier proper 1. There will therefore be,in general, no need to provide protective films surrounding therectifying junction. Further, with the ring 10 positioned as shown, itacts as a shield to prevent brazing vapours produced during the finalbrazing operations of manufacture from reaching the rectifying junction.

The modification shown in Figure 2 will be largely self-evident from thefigure. As will be seen, the essential difference between thearrangement of Figure 2 and that of Figure 1 lies in the somewhatdifferent shape and positioning of the solidified desiccant body whichin Figure 2 is referenced to 10 In Figure 2, the desiccant body 10- is acylinder mounted with one end in a ring recess in the top face of theheat-sink base 2. It projects up between the parts 4 and 5 and as willbe observed provides a high degree of protection of the rectifier proper1 against possible vapours produced during the final brazing operations.

I claim:

1. A semi-conductor rectifier assembly comprising a rectifier propermounted in a hermetically sealed envelope having metal parts, areas ofwhich have been fixed to one another by a process involving theapplication of high temperature heating, and wherein a pro-cast body ofsolidified desiccant material is positioned between the rectifier properand said areas at which said parts are so fixed to one another.

2. An assembly as claimed in claim 1 wherein the desiccant material isaluminium sodium silicate which has been subject to molecular sievingand solidified.

References Cited in the file of this patent UNITED STATES PATENTS2,686,279 Barton Aug. 10, 1954 2,820,931 Koury Jan. 21, 1958 2,858,356Setchell Oct. 28, 1958

